No abstract

BackgroundOsteosarcoma is a bone-forming tumor of mesenchymal origin that presents a clinical pattern that is consistent with the cancer stem cell model. Cells with stem-like properties (CSCs) have been identified in several tumors and hypothesized as the responsible for the relative resistance to therapy and tumor relapses. In this study, we aimed to identify and characterize CSCs populations in a human osteosarcoma cell line and to explore their role in the responsiveness to conventional therapies.MethodsCSCs were isolated from the human MNNG/HOS cell line using the sphere formation assay and characterized in terms of self-renewal, mesenchymal stem cell properties, expression of pluripotency markers and ABC transporters, metabolic activity and tumorigenicity. Cell's sensitivity to conventional chemotherapeutic agents and to irradiation was analyzed and related with cell cycle-induced alterations and apoptosis.ResultsThe isolated CSCs were found to possess self-renewal and multipotential differentiation capabilities, express markers of pluripotent embryonic stem cells Oct4 and Nanog and the ABC transporters P-glycoprotein and BCRP, exhibit low metabolic activity and induce tumors in athymic mice. Compared with parental MNNG/HOS cells, CSCs were relatively more resistant to both chemotherapy and irradiation. None of the treatments have induced significant cell-cycle alterations and apoptosis in CSCs.ConclusionsMNNG/HOS osteosarcoma cells contain a stem-like cell population relatively resistant to conventional chemotherapeutic agents and irradiation. This resistant phenotype appears to be related with some stem features, namely the high expression of the drug efflux transporters P-glycoprotein and BCRP and their quiescent nature, which may provide a biological basis for resistance to therapy and recurrence commonly observed in osteosarcoma.

Osteosarcoma is a bone tumor, displaying significant cellular and histological heterogeneity and a complex genetic phenotype. Although multiple studies strongly suggest the presence of cancer stem cells in osteosarcoma, a consensus on their characterization is still missing. We used a combination of functional assays (sphere-forming, Aldefluor, and side-population) for identification of cancer stem cell populations in osteosarcoma cell lines. Expression of stemness-related transcription factors, quiescent nature, in vivo tumorigenicity, and Wnt/β-catenin activation were evaluated. We show that different cancer stem cell populations may co-exist in osteosarcoma cell lines exhibiting distinct functional properties. Osteosarcoma spheres are slowly-proliferating populations, overexpress SOX2, and KLF4 stemness-related genes and have enhanced tumorigenic potential. Additionally, spheres show specific activation of Wnt/β-catenin signaling as evidenced by increased nuclear β-catenin, TCF/LEF activity, and AXIN2 expression, in a subset of the cell lines. Aldefluor-positive populations were detected in all osteosarcoma cell lines and overexpress SOX2, but not KLF4. The side-population phenotype is correlated with ABCG2 drug-efflux transporter expression. Distinct functional methods seem to identify cancer stem cells with dissimilar characteristics. Intrinsic heterogeneity may exist within osteosarcoma cancer stem cells and can have implications on the design of targeted therapies aiming to eradicate these cells within tumors. J. Cell. Physiol. 231: 876-886, 2016. © 2015 Wiley Periodicals, Inc.

No abstract

No abstract

No abstract

This preclinical study suggests that Metformin may be a potentially useful therapeutic agent and chemosensitizer of osteosarcoma stem-like cells to doxorubicin.

Osteosarcoma is amongst the most prevalent bone sarcomas and majorly afflicts children and adolescents. Therapeutic regimens based on the triad of doxorubicin, cisplatin and methotrexate have been used as the state-of-the-art approach to clinical treatment and management, with no significant improvements in the general outcomes since their inception in the early 1970s. This fact raises the following problematic questions: Why do some patients still relapse despite an initial good response to therapy? Why do nearly 30% of patients not respond to neoadjuvant therapies? Does residual persistent disease contribute to relapses and possible metastatic dissemination? Accumulating evidence suggests that chemoresistant cancer stem cells may be the major culprits contributing to those challenging clinical outcomes. Herein, we revisit the maneuvers that cancer stem cells devise for eluding cell killing by the classic cytotoxic therapies used in osteosarcoma, highlighting studies that demonstrate the complex crosstalk of signaling pathways that cancer stem cells can recruit to become chemoresistant.